American-Russian Roy Jones Junior suffered another career setback on Saturday as he was knocked out in the fourth round of a cruiserweight bout against Welshman Enzo Maccarinelli, in Moscow.

The defeat is Jones, a man once regarded as the greatest pound for pound fighter in the world, in the 1990s, ninth career defeat and fifth by Knock-out.

Jones, 46, was granted Russian citizenship in September.

Ever since a shocked second round KO defeat to compatriot Antonio Tarver for the lineal light-heavyweight title in 2004, Jones has been a shadow of his former self.

He came into the Maccarinelli bout on the back of an eight-fight winning streak, although only against overmatched opposition, since a brutal 10th round KO defeat to Russian Denis Lebedev in Moscow in 2011.

Former WBO cruiserweight titlist Maccarinelli, 35, has not held a world belt since losing that strap to compatriot David Haye in 2008.

*Photo shows Jones (L) and Maccarinelli (R) during their weigh-in.